A wireless local area network (WLAN) basically supports a basic service set (BSS) mode including an access point (AP) serving as a connection point of a distribution system (DS) and a plurality of stations (STAs), not APs, or an independent BSS (IBSS) mode including only stations (STAs) (hereinafter, AP and STA will be referred to as a ‘terminal’).
In a communication system such as a WLAN, or the like, a frame (or a data frame) and length information regarding the length of the frame are exchanged between a media access control (MAC) layer and a physical (PHY) layer. In order to inform a receiver (or a receiving end) about the end of the frame, the PHY layer of a transmitter (or a sending end) includes a header having the information regarding the length of the frame in the frame and transmits the same, or adds a delimiter including information indicating the end of the frame in the end of the frame. Accordingly, in the PHY layer of the receiver recognizes the end of the received frame by using the length information or the delimiter information having a particular format included in the received frame.
An international standard of the WLAN by IEEE 802.11 defines a data unit processed in the MAC layer, as a MAC protocol data unit (MPDU). When the MPDU is transferred from the MAC layer to the PHY layer, it is called a PHY service data unit (PSDU). The information regarding the length of the frame for recognizing the end of the frame is transferred, along with the PSDU, from the MAC layer to the PHY layer. The PHY layer of the transmitter transmits the information regarding the length of the frame together with the data to the receiver. A decoder of the PHY layer of the receiver restores the MPDU included in the PSDU by the length indicated in the length information by using the length information included in a signal symbol of a physical layer convergence protocol (PLCP) preamble of the received frame, and transfers the restored data and length information to the MAC layer.
For communication based on the standard IEEE 802.11, various methods are used for the transmitter to transfer length information to the receiver. For example, in 802.11b, a PLCP header includes time information having a size of 16 bits, and in 802.11a/g, an L-SIG field of a PLCP preamble includes length information having a size of 12 bits representing the length of a frame by byte. Also, in 802.11n, an HT-SIG field of the PLCP preamble includes length information having a size of 16 bits representing the length of an MPDU or an A-MPDU (Aggregated-MPDU) of the MAC layer by byte.